Ion mobility spectrometers (IMS) are widely used for analyzing ionized compounds by their mobility, which is the function of ion charge, mass and shape. Typical IMS comprises an ion source for soft ionization of analyte compounds, an ion gate (typically Tyndal gate) to form short ion packets, a gas filled drift tube for ion separation in electrostatic fields, and a collector to measure time dependent signal. As a standalone analytical technique, IMS has a generally low resolution (substantially at or between 50-100). IMS has been primarily considered as a low cost hand-held system and method for detecting toxic volatile compounds, as it has a generally low detection limit that can be enhanced by utilizing specific ion molecular reactions with doping vapors. More recently IMS has been coupled with gas chromatography (GC), liquid chromatography (LC) and mass spectrometry (MS), where IMS brings an additional dimension of analytical separation. However, the straight forward coupling can yield strong signal losses in IMS due to at or about ˜1% duty cycle of a Tyndal ion gate and a mismatch in gas pressures and ion cloud size between IMS and MS. In addition, employing scanning MS (e.g., quadrupoles and the like) there is a mismatch in time scales.
U.S. Pat. No. 5,200,614, incorporated herein by reference in its entirety, discloses an improvement to IMS sensitivity by trapping ions between gate pulses. U.S. Pat. No. 3,902,064, incorporated herein by reference in its entirety, discloses a combination using an IMS spectrometer with a downstream mass spectrometer for complimenting mobility measurements by ion mass measurements. Young et al., in paper J. Chem. Phys., v. 53, No 11, pp. 4295-4302, incorporated herein by reference in its entirety, discloses a combination using an IMS spectrometer with a downstream orthogonally accelerating time-of-flight detector that is generally capable for fast recordation of panoramic (all mass) spectra for higher speed and duty cycle of mass measurements. U.S. Pat. No. 5,905,258, incorporated herein by reference in its entirety, discloses a combination of both features—an ion trap in-front of the IMS and an orthogonal TOF past IMS, thus capitalizing on both advantages—higher duty cycle of IMS and MS.
U.S. Pat. No. 6,107,628, incorporated herein by reference in its entirety, discloses an ion funnel device for converging ion flows at intermediate gas pressures. U.S. Pat. No. 6,818,890, incorporated herein by reference in its entirety, discloses an ion funnel for ion confinement past IMS. Paper Anal. Chem., 2008, v. 80, pp. 612-623, incorporated herein by reference in its entirety, describes using an ion funnel device for both—for ion trapping prior to IMS and for ion confinement beyond the IMS. Details on the so-called hourglass ion funnel trap are also presented in Anal. Chem., 2007, v. 79, pp. 7845-7852, incorporated herein by reference in its entirety. The described method presents the ultimately sensitive IMS-MS from the prior art, which still generally suffers several limitations. The number of trapped ions is limited by the space charge capacity of the ion trap and of IMS drift tube to at or about 1E+7 charges per pulse which is normally accumulated in at or around 1 ms time. Both—the hourglass gate and downstream ion funnel do spread ion packets to substantially at or between about (200-400) μs, which slows down the IMS speed, requires long drift separation time of substantially at or between about (20-40) ms, requires constructing long (about 1 m long) IMS drift tubes, and limits the IMS duty cycle (at or about 1 ms of gate saturation vs. at or about 40 ms cycle), charge throughput, and the dynamic range.
WO2008112351, incorporated herein by reference in its entirety, discloses a method of improving IMS dynamic range and space charge capacity by multiplexed coding of the ion trap which operates at much higher net frequency compared to conventional regime of single trap firing per IMS separation. However, the approach can cause ion packets overlapping and confusions at data interpretation. In order to match IMS separation time the employed downstream orthogonal TOF has at or about 100 μs pulse period and hence has limited resolution (at or about R=5,000).
Summarizing the above, IMS and IMS-TOF of prior art are limited in their charge throughput, dynamic range, speed, and resolution, which limits their combination with fast separation methods. Therefore, improving IMS and IMS-TOF parameters is beneficial as described herein.